Oscar Diggs (James Franco) is an ambitious illusionist/con man employed by a midwestern traveling circus. Despite being greatly ambitious, Oscar's magic career isn't taking off. His illusions are cheap, his suits are torn and patched, and he's barely making enough money to keep his head above water. Frank (Zach Braff), Oscar's circus assistant, barges into Oscar's caravan as he puts the moves on his latest magician's assistant May (Abigail Spencer). He produces a small wooden music box, which he claims once belonged to his great-grandmother, and gives it to May as a token of his love. Frank reminds Oscar, or Oz, as he's known, that his next show is about to begin. Frank hands Oz the show's cash takings: an old hat filled with a dozen quarters and nickels. Oz reluctantly plucks a pair of coins from the hat and gives them to Frank, and pockets the rest. Frank is unhappy with how Oz treats him.

The magic show begins with Oz striding out onto the stage in a mystical, quasi-oriental robe and turban A young girl in a wheelchair in the front row (Joey King) watches in awe as Oz calls for a volunteer. A dozen hands shoot up, but none belong to May, Oz's assistant and ringer for the show. Oz finally calls May to the stage, much to the bewilderment of the crowd, and she takes the stage. Backstage, Frank produces all of the practical effects for the show: playing music, setting off pyrotechnics, etc. On stage Oz puts May into a deep sleep and causes her unconscious body to float in mid air. An irate voice shouts something from the back: "I see a wire!" Another voice joins in: "Yeah! I see two of 'em!" Bright lights are cast onto the stage, and sure enough, two very visible wires are seen suspending May's body from the ceiling "I want my money back you fraud!" Oz gestures to Frank, who tosses him a scimitar. Oz flicks the scimitar between his hands and then violently cuts the visible wires.... but May remains floating. The crowd gasps and Oz, for the finale, whips the silk sheet off of May's body, revealing empty air. The crowd applauds in unison, and Oz happily accepts the "Bravos!" and "Encores!", and then a small voice cuts through the cheers: "Make me walk!" All goes silent. The little girl in the front row, in the wheelchair, pushes herself toward the stage and repeats her pleas "Please, Wizard. Make me walk!" Oz, caught off guard by the unscripted request, seeks a diplomatic or heartfelt response, but all that comes out is "I'm not that kind of wizard, kid." The crowd turns on him, booing and hissing. Oz, who is now being pelted by popcorn and peanut shells, tells Frank to close the curtains.

Outside, the circus-folk are hurriedly packing up the traveling circus as gray clouds swirl above them. Frank takes Oz aside and tells him that a certain lady-friend is waiting for him in his caravan. He sidesteps the chaos, enters his caravan and is surprised to see a young blonde woman, and not May, waiting for him. This is Annie (Michelle Williams); one of Oz's old romances he met on the road. She's come to see Oz because another man proposed to her and she wanted to tell him first. The pair's chemistry is obvious, but Oz's philandering has ruined anything they might have had. Outside, May watches as another brunette, close to her age, bursts out of a tent holding a music box identical to the one Oz gave her. She swiftly realizes that Oz used her. Seconds later an angry strong-man, the woman's husband, comes bursting out of the tent, hell-bent on tearing Oz a new one. The strong-man crashes through Oz's caravan wall and chases Oz all through the fairground. Oz manages to sneak aboard a readied hot air balloon and escape the clutches of the strong-man. As he soars away Frank throws Oz his hat and magician's bag, filled with his various illusionary instruments. From above Oz watches as all the circus folk fearfully run away, and then he sees it: a massive tornado which is sucking him in. Oz pins himself as tightly as possible into the balloon's basket as the entire contraption is violently whipped back-and-forth inside of the tornado.

After nearly being impaled dozens of times, Oz and the balloon escape the violent winds of the twister and emerge in the colorful, widescreen World of Oz. Oz and the balloon luckily avoid hitting the giant mountains surrounding them, but the balloon ultimately crashes, and Oz unceremoniously lands in a shallow river. Oz, bewildered, finds himself surrounded with gigantic sentient plants and small mischievous fairies which peck at his legs. He calls out for help, and through the bushes appears the beautiful and alluring Theodora (Mila Kunis). Theodora answers him and Oz, struck by her beauty, puts on the charm. He tells her that his name is Oz, and she is shocked -- the prophecy foretold that a wizard named Oz (the name of their land) would return to Oz and save them from the Wicked Witch. Oz, jokes that all witches must be green, warted, and must ride a broom, to which Theodora responds "but I'm a witch." She explains that there are good witches and wicked witches, and that she is simply a good witch. Mysterious growling echoes from the forest nearby and Theodora, recognizing the sound of the Wicked Witch's minions tells Oz to hide. The pair disappear into an alcove and watch as a frightening winged howler monkey swoops in and searches for them. Oz, thinking quickly, reaches into his top hat and retrieves a white dove which he releases into the air. The howler monkey, seeing the bird, flies off after it. Oz and Theodora escape and begin their trek to the Emerald City.

Oz uses his charms to appeal to Theodora, and she soon falls in love with him. She tells him that as the new Wizard of Oz, he will soon become the land's new king and that, if he will allow it, she will be his queen. As a token of his love, Oz gives Theodora a wooden music box -- the same type of box given to May and countless other women he met over the years. The pair walks toward the Emerald City and soon come across a winged Capuchin monkey tangled in a mass of man eating plants. Theodora implores that Oz help the monkey and Oz, eager to impress his new girl, frees the monkey, named Finley (Zach Braff) from the weeds. Oz soon realizes that the plants were not the true threat. A massive lion appears, about to pounce on Oz and Finley. Oz, without thinking, reaches into his jacket pocket and tosses a handful of powder to the ground. Thick red smoke explodes from the ground and frightens the cowardly lion away. Theodora, now convinced that Oz is the true wizard of the prophecy, hugs him. Finley, thankful for Oz's intervention, offers his servitude to Oz for life. Finley explains that as a debtor to Oz, he must do anything and everything Oz says. Oz immediately tells the shocked Finley that he is not the Wizard that Theodora thinks that he is. He's just a con man, with a few illusions and tricks up his sleeve. Finley is disappointed to hear this news, but doesn't tell Theodora. Oz hands his heavy bag to Finley and tells him to follow them. The trio soon meets a large caravan of horses and soldiers along a yellow-brick road. Their leader, Knuck (Tony Cox) does not believe Oz is the great wizard Theodora says he is. Oz talks down to Knuck, calls him "sour puss" and tells him to obey his king. Oz and Theodora jump into a carriage and are whisked away to the Emerald City. Inside the city Theodora introduces Oz to her sister Evanora (Rachel Weisz) -- a young brunette witch with a green sapphire necklace around her neck. Both wise and beautiful, Evanora looks at Oz with skepticism. She and Theodora take him to the throne room, which Oz treats with little reverence. Evanora chides the gullible Theodora for believing that Oz was the wizard from the prophecy, but agrees to humor Oz until she can fully prove that he's a fraud.

Evanora takes Oz to the King's vault: a massive chamber overflowing with gold and riches, all property of the King of Oz. Oz excitedly dives into the piles of gold while the ever skeptical Evanora look on. She reminds Oz that the vault is the property of the King of Oz, which he will be only when he kills the Wicked Witch. Oz, realizing that his Kingship comes with strings attached, drops the gold and begins to believe that he'll never be king. Evanora soothes him and explains that killing the Wicked Witch won't be difficult. All that's required is breaking her wand; break the wand, kill the witch, that's it. Bolstered by this new found information, Oz readies himself to go find the witch.

With Finley in tow, Oz heads off to the dark woods to find and kill the Wicked Witch. Along the way the pair happens across a recently devastated town. The entire city is made of porcelain: porcelain houses which look like gigantic teapots, porcelain trees, and porcelain residents. It's all too spooky. They hear crying inside of one of the few still-standing houses. Inside they find a tiny, young porcelain girl who, after the attack, was broken. Her legs were separated from her body, and she's unable to move. Oz comforts the China Girl (Joey King) and produces, from his bag, a small bottle of instant-dry glue. He repairs her shattered legs and helps her get to her feet. She happily thanks Oz and Finley and tags along with them on their journey. The trio comes to a fork in the road; turn left for the Emerald City, turn right for the dark woods. Oz tells the China Girl to walk to the Emerald City and tell Evanora that she is a friend of Oz. The China Girl throws a fit, and refuses to leave Oz as her family and friends are broken and dead, and he's the only friend she's got. Oz allows the China Girl to follow them to the dark woods.

The Dark Woods are frightening. Twisted, violent plants try to impale the trio as they make their way deeper into the forest. They finally come to a cemetery and see a dark, hooded figure trying to enter. They quickly realize that the figure must be the Wicked Witch, and watch as the figure carefully places its wand onto a pile of boxes nearby. While Finley distracts the figure, Oz sneaks over to the wand, takes it and is about to break it in two when a soothing voice stops him. The hooded figure unveils herself, revealing a beautiful blonde face beneath it, identical to Annie (Michelle Williams). She introduces herself as Glinda and explains that the true Wicked Witch is back at the Emerald City. Evanora, years ago, sought to rule Oz by herself and killed their father, the King, so she could rule uncontested. When rumors swelled that the Wizard of Oz would return and take his place as King, Evanora vowed to never let that happen. She'd trick the Wizard into killing the sister who opposed her, Glinda, and then kill the Wizard herself so that she could rule Oz forever. When Glinda learned of Evanora's treachery, she left the Emerald City and spent every day at her father, the King's, grave. Back in Emerald City Evanora watches, in her crystal ball, as her plans to kill Glinda failed. Angered, Evanora sends out her armies to stop and kill Oz and Glinda. Back in the graveyard, the quartet of Oz, Glinda, Finley and China Girl hear the stomping of boots approaching. Evanora's army marches through the graveyard, intent to kill them. Glinda pleads with Oz to do something magical to stop the army and Oz, being nothing more than a con man illusionist, asks her to care of it. She takes her wand and draws thick fog out of the ground, blinding the army of Winkies and baboons. The quartet finds themselves at the end of a cliff, hanging over a bottomless pit and Glinda, with no other option, leaps off the cliff. With the army quickly approaching Finley, China Girl, and finally Oz fall after her. The four appear, moments later in gigantic floating soap bubbles, which send them flying miles away. In the distance, Oz sees and inquires about a small city encapsulated within a giant, soapy bubble. Gilda explains that the bubble is a protective barrier, which keeps out anybody with evil or malcontent in their heart. Oz, being both slightly evil and malicious himself, fears that he won't be able to get through. Glinda, Finley and China Girl easily glide through the bubble barrier, but Oz, after bouncing off the of barrier a few times, is finally able to squeak through.

In Emerald City, Evanora is not pleased with Oz and Glinda escaping her grasp. She concocts a plan. She invites Theodora into her quarters and magically produces a small wooden music box identical to the one Oz gave Theodora. Theodora, upon seeing the music box, is hurt by Oz's presumed betrayal and returns to her room. She sits in front of her vanity mirror and cries. Her tears are like acid, etching permanent burns into her skin.

Glinda introduces Oz to the people of the quaint city within the bubble: farmers, tinkerers, munchkins, etc. They all live in innocent, unspoilt happiness and are very excited to meet and hear from the wizard of myth and prophecy. Oz, now convinced that his rouse has gone too far takes Glinda aside and explains that he is not a real magician. He's a fake, a charlitan, an illusionist who can't perform real magic. Glinda, to Oz's surprise, admits that she knows. She knew from the moment she first met him, but just because she knows doesn't mean that the townspeople need to. With this new information, Oz puts on a show of confidence, convincing the townspeople that he is the wizard they hoped would return to destroy the Wicked Witch.

Theodora's anger at Oz is at a boiling point, as is evidenced by her severely disfigured, acid-burnt face. Evanora, now in total control of Theodora convinces Theodora to follow along with her plan and become more powerful than any wizard ever. Evanora produces a small, green apple and tells Theodora that the apple will give her the power to kill Oz. She bites into the apple and soon keels over. Her skin darkes, her voice deepens, and her silhouette grows tall and evil. Theodora grabs a black brimmed hat and laughs maniacally. A mysterious storm cloud appears over Glinda and Oz's town. A red-hot light at the center of the cloud pounds against the "impenetrable" bubble surrounding the town. The cloud pounds against the bubble again and again until it breaks like an egg. The red-hot light beams into the city, landing like a meteor in the town square. A glowing evil figure emerges from the crater -- it's Theodora, transfigured into a green-skinned, black-suited old witch. She confronts Oz, and explains that she has become a truly Wicked Witch because of his treachery. She steals a broom from a townsperson and rides away, leaving a trail of black smoke behind her. Amidst the chaos, Glinda searches for Oz, but finds that he's run off. She confronts him in his quarters, where he's quickly packing his bags for a hasty escape. Glinda tries giving Oz the confidence to believe in himself, and to look past the fact that he's not a real wizard. Through soul-searching, Oz formulates a plan. He tells Glinda to gather the town's smartest and strongest. Oz meets with the town's Master Tinker (Bill Cobbs) and his men, the appointed scientists of the city, and together they plan an illusion to trick Theodora and Evanora. Under Oz's guidance the townspeople create elaborate mechanisms for the show. Oz shows the tinkers how to create a movie projector, how to create black powder, and finally how to build a hot-air balloon. Oz asks the head Tinker to keep the balloon a secret. He and Glinda, together, form a battle plan. They look at a map of the Emerald City and its outlying areas. Oz suggests that they enter the city through the Poppy fields, but Glinda explains that the poppy fields will put anyone who breaths in their spores, into an inescapable deep sleep. Oz thinks of a way to use this to their advantage. Finally, Glinda reveals that she has a contact to get them into the city unnoticed. Knuck, AKA Sour puss, appears and reveals himself to be their inside man.

The assault on Emerald City begins. Oz, along with Knuck and other munchkins, disguise themselves and sneak passed an unwitting Winkie Gate Keeper (Bruce Campbell). They sneak the carriage, filled with the projection equipment and Oz's balloon, into the city. As soon as they pass through the gate, Oz separates himself from the group, with the balloon, and sneaks up to the King's vault, and begins filling the hot-air balloon's basket with gold. Down on the ground, Finley, Knuck and the Master Tinker see that Oz has betrayed them, in favor of escaping with a balloon full of gold, but continue with the plan. Out at the edge of the city Glinda casts a spell which send thick fog across the landscape. Theodora and Evanora, distracted by the thick blanket of fog, watch as an army of soldiers stomps through the fog, toward the city. The pair of witches sends out their entire army of baboons to stop the incoming force. The baboons tear-into the soldiers, but are shocked to find that they're full of hay. The fog dissipates, revealing that the soldiers are mechanical scarecrows, built by the townspeople, and to make matters worse, the fog was covering the poppy field. Almost all of the baboons fall into a deep sleep, leaving the city mostly defenseless. The townspeople disappear back into the woods as a few conscience baboons go after them. Glinda is suddenly taken hostage by a pair of them. She drops her wand into the field and is taken up into the center of the city. Evanora searches the grass for the wand, but thanks to the China Girl, is unable to find it. Evanora flies back into the city, and at its center is met by Theodora. The pair stand on either side of Glinda, who has been chained to a pair of posts. The angry citizens of Emerald City watch on in horror as Evanora and Theodora torture Glinda with lightning and fire attacks. Above them, Oz's balloon appears. Evanora points at the balloon, and exposes Oz as a greedy fraud, trying to escape with the town's riches instead of defending the town as the prophecy foretold. Evanora angrily shoots fire at the hot air balloon, exploding it, and sending the riches crashing down to the ground in a giant plume of black smoke. Glinda, shocked by Oz's death, cries, and prepares to die. Suddenly a booming voice echoes throughout the city and Oz's ghostly face appears on the plume of smoke. He explains that his death was necessary to become the true Wizard of Oz, and that he is now immortal and all-powerful. Evanora and Theodora are speechless. They fire lightning and fireballs into Oz's ghostly facade, but they do nothing. Secretly, Oz, Knuck, Finley, and the Master Tinker sit huddled in the caravan at the center of the city, projecting a moving image onto the black smoke, putting-on a spectacular illusion. While distracted, the China Girl sneaks Glinda her wand and manages to break her free. Upon finding Glinda gone, the townspeople turning on her, and a massive floating head in the sky, Evanora escapes into the castle, leaving Theodora to deal with the town by herself. Soon Oz, and the townspeople, rain fireworks down onto Theodora, forcing her to escape on her broom. As she trails into the distance, she promises to return and stop Oz for good.

Evanora, inside the castle, is confronted by Glinda seated in her father's throne. Evanora shoots lightning at Glinda, but Glinda deflects the attacks with her wand. The fight starts on the ground but ends in the air. Evanora grabs Glinda by the throat, and Glinda grasps at Evanora's chest. Their attacks rebound off one another and the two land, painfully, on the ground. Evanora prepares to deliver the killing blow, but lacks the magic to do so. She reaches for her neck, the emerald necklace that had been around it, the source of her power, is gone; shattered into a thousand pieces on the ground, under Glinda. Evanora suddenly keels over. Her beautiful features disappear. Her nails grow long and dirty, her skin becomes wrinkled and liver-spotted, and an old hag appears in her place. The old, true Evanora lunges at Glinda, but Glinda, with wand in hand, repels her attack and sends her flying through the castle window. She's caught by a pair of flying baboons and carried off into the distance.

The Emerald City, now freed of tyranny, celebrates. Glinda walks into the throne room and is greeted by the smokey visage of Oz, hovering over the throne. Finley latches the door. China Girl and Knuck close the curtains and once the coast is clear, Master Tinker switches-off the mechanism and out steps Oz, in the flesh. As thanks for their exemplary work, Oz gives each of them a gift. To Master Tinker, he gives a swiss-army knife, complete with a fork and spoon. To Knuck, AKA Sour Puss, he gives a novelty mask with a smile painted on it. To Finley he gives his top hat and friendship, and to China Girl he offers themselves as her new family. Finally, to Glinda, he takes her behind the curtain and plants a giant kiss on her.